The invention relates to a process for the production of thermoplastic moulding compounds (compositions), in particular for the production of acrylonitrile-butadiene-styrene (ABS), wherein at least a first reagent (component) and a second reagent (component) of the thermoplastic moulding compound are fed to a gear pump. The invention also relates to a thermoplastic moulding compound that is produced by the inventive process.
It is known from the prior art to produce thermoplastic polymers, such as acrylonitrile-butadiene-styrene (ABS) by means of an extruder, in particular by means of a twin-screw extruder. In this case, the reagents, in particular styrene-acrylonitrile copolymer (SAN) and a polybutadiene based rubber, are fed to an extruder. The rubber can be present in the form of SAN-grafted rubber, respectively of SAN-grafted elastomer. Within the extruder, the reagents are melted and mixed, and/or dispersed, to form a dispersion and to form a moulding compound or a polymer blend. In this case, the rubber feed, in particular in the form of SAN-grafted rubber or SAN-grafted elastomer, is dispersed in a styrene-acrylonitrile matrix. Also other means for producing thermoplastic polymers are known, for example single screw extruders, kneading machines or banbury sheet compounding units.
WO 2009/103714 discloses a twin-screw extruder for extruding moulding compounds. The twin-screw extruder comprises in this case two screws which are accommodated in a barrel and which rotate in the same direction. The twin-screw extruder further comprises a feed zone, a transition zone and an output zone. The reagents are fed as moulding compound to the feed zone, which for this purpose has a charging opening.
The moulding compound can be fed in this case in solid form, in particular as granules, but also molten, and therefore viscous, to the feed zone. The moulding compound is t aken into the feed zone by means of the two screws, transported further and compressed. In the transition zone which follows the feed zone, the moulding compound is melted and homogenized. In the output zone, further homogenization of the moulding compound which is present as melt proceeds. Optionally, further residues present of solid particles are also fused. In addition, the material components are uniformly distributed. Also, the temperature of the melt is made uniform. In addition, in the output zone, a pressure necessary for extrusion through an extrusion die is built up.
WO 1998/13412 describes screw machines which have at least one pinch-off section having at least one baffle element and an associated dewatering opening upstream of the first baffle element. In addition, the screw machines contain degassing sections which are situated downstream of the last plasticizing section. The degassing openings and dewatering openings can be provided with a device which prevents escape of extrusion material. Retention screws are described as preferred for this purpose.
The degassing and dewatering of thermoplastic moulding compounds by means of screw machines is also known. EP-A 0735077 describes a process for the production of impact-modified thermoplastics by mechanical dewatering of an elastomeric component and mixing with a thermoplastic polymer in a screw machine. The dewatering openings are provided with retention screws and are operated at overpressure.
JP S02-286208 (1990) discloses three different dewatering processes by means of an extruder which is equipped with two screws. Moisture in liquid form and additionally in gaseous form is withdrawn from the extrusion mix in each case via Seiher barrels.
Document JP H57-167303 (1982) describes that an extrusion mix, in this case, e.g., slurries of polymer particles, is metered into a twin-screw extruder, dewatered, degassed and kneaded. Upstream of the compression zone, water can escape from the extruder in liquid form. Residual moisture can escape in gaseous form. Seiher barrels are used as dewatering openings.
JP H60-222223 (1985) discloses a process in which water in liquid form is withdrawn from an extrusion material, preferably a food, but also other materials. The dewatering proceeds by means of a twin-screw extruder. The moisture is discharged backwards through an opening which is attached to a vacuum pump.
A device for the extrusion of thermoplastics, in particular a screw machine, proceeds from WO 2004/028781. The device in this case comprises a degassing opening and a dewatering opening which is equipped, for example, with a metal wire cloth.
JP 2011 132 426 A discloses a method for producing rubber-reinforced thermoplastic resin composition. Thereby, reagents are supplied to a loop type reactor containing a pump and an external loop structure.
WO 2015/000873 discloses a process for the manufacturing of ABS-molding compositions. Thereby, a elastomer component, a thermoplastic polymer, a further polymer and additives are mixed in an extruder, comprising the steps of precipitating the elastomer component and mechanical dewatering of the elastomer component which leads to improved salt-free products.
In DE 28 46 757, a method for sintering of styrene-acrylonitrile graft polymers from dispersions is disclosed. The process is carried out in a tubular reactor, in particular in an extruder. In U.S. Pat. No. 3,851,014, a method for making rubber modified resins using a static mixer is disclosed.